Thread Bar Project, nothing is going right and I need help

[jlsmithseven]

That's tighter than it has to be. Back off pressure. Just snug it so there is no axial play; it will get tighter as the part heats up.

EDIT: I forgot that you're moving from lathe to lathe. Now that you've re-drilled your centers, don't forget to re-cut the taper on your headstock dead center after mounting it in the new lathe; this will get it concentric with the spindle.

Let us know how it goes.

yes i re cut it every time. thanks for the help. i appreciate it.

 

[Randall Marx]

Yes, I think you might have found the problem. You described recutting the center and that there was a piece of crap (swarf, dirt, general crud) present. That would cause a problem like you are seeing. Hopefully that is the problem. If it is, the lesson is to make sure your centers are clean before mounting workpiece.

 

[bfd]

you can chuck up your part and indicate the of near the end and single point cut the center on each end. run a last word type indicator in the center hole after you recut the center. don't use a center drill because it will just follow the existing hole runout and all. after you recut your centers then reinstall the bar on centers and indicate the of of the bar. if its out then recut it. now you have the bar as true as it can be. thread from there. ps your threaded bar is a lot easier than the one I had to do you have all standard threads. I did on standard thread 3/4"-10 then a two lead left handed a 3 lead right handed and a 4 lead left handed acme plus the nuts to fit each one. bill

 

[chips&more]

So very sorry to read about your frustration. Learning the skill of a machinist is one thing. Instructor’s lack of communicating is another. The instructor should be offering you help. Even with all of the folks at HM and there combined knowledge at your service. It’s hard to find your problem without pics or better yet being there to see firsthand. If you want, you can have the instructor PM me personally…Dave

 

[jlsmithseven]

So, first I'd like to thank you all for working so hard helping me figure this out.

I have good and bad news today, ultimately good news overall though.

So I went into shop today and took all your suggestions and combined them and sure enough, it was turning true again. First, I re-cut my center at 60 degrees. Then, I lubed the dead center and live center. I put my piece in and tightened it, not too hard this time, just enough. Turned on the lathe and to my amazement the piece was turning perfectly true and not wobbling. Step 1, done.

Step 2, check for tailstock runout. It was .004 out so I adjusted the tailstock and got it within .001 difference, so that was a win.

Step 3, which should have been set my tool height, didn't go so well. I was running my 60 degree thread cutting tool a bit too high the entire time in shop today and couldn't figure out why my piece was just hitting the end and bumping back in. One time, it caught the end and jammed the tool bit into the piece so I had to stop the machine. I had to find my threads again with the help of others. So I kept cutting passes of about .010-0.015 per pass. Eventually right before break, my machine jammed again. Then I told a co-student about the problem and he asked if my tool height was right. I said, wow I forgot to set it..

So I come back from break, set my tool height correctly and sure enough the threads were cutting much nicer. The biggest issue here was, I couldn't re-find my threads correctly. I used the compound in-feed to just scrape the right side of the thread, etc...then.... I noticed that the thread cutting tool was only cutting threads on the left side of my external threads. I should have stopped it there, but I kept going. Eventually I got to the end of the thread, like 60 passes later, got to my tolerance and saw there was a small lip to the left of my threads. Sure enough the nut didn't thread on and my piece was ruined so I have to start over because it's a 100% or 0 project.

So in all, it was quite the learning experience. The next time I am going to set my tool height and take everything I've learned today to heart. But I thank you guys again for your help and I very much appreciate it. I'll be sticking around on this forum for a while. I'll keep you guys posted and eventually get some more pics and stuff to share. My instructor has helped me throughout these issues and I'm just learning through each mistake. Hopefully I've learned all I need to so far for this project because it's been a LOT.

 

[Mark_f]

What I see here , is you are doing the most important thing...... LEARNING. We have all been in your place at one time in our life. Keep learning as you go. You will probably learn more from your mistakes than from anything else. You may forget accomplishments, but you will never forget the little mistakes. Soon you will be amazed what you can do with the new knowledge you are getting.

 

[Tozguy]

Good on you Mr. Smith, we are proud of you.

 

[rwm]

I am not sure how the other guys feel, but when I am cutting threads I never cut deeper than .005 at a time.
What is the best way to re-capture the thread? Meaning re-synchronize your lead screw? I have one it by engaging the lead screw and adjusting the compound and cross slide to fit into the thead. Any other ideas?
Robert

 

[T Bredehoft]

engaging the lead screw and adjusting the compound and cross slide to fit into the thread.

don't forget to hold the saddle to the right, against the lead screw when "finding" the thread.

hold the saddle to the right corrected by Tozguy, Thanks for catching that!

 

[woodchucker]

Also I use the compound to feed in depth, so I only cut on the left side of the thread. I used to do it via the cross slide only, but I never found the threads to be as nice as only compound.
Compound is 1 edge mostly cutting
X Slide is both edges cutting and that puts more pressure on the tool and the piece.